Method of obtaining photographic contrasts by means of diazonium compounds



rsientedjs e .18, 1934 1.07am v 00 oomormn OI OBTAINING PHOTOGRAPH!T8831 MEANS 01" DIAZONIUM Boeloi'hnflendrikflinkandlanllendrikde Boer,Eindhoven, Netherlands, alclgnors to N.

vi Netherlands Serial vember 10, 1931 Drawing. Application November 10,

No. 642,124. In the en, limlhoven,

1932, Netherlands No- -7 Claims. (01. 95-7) The present inventionrelates to improvements in the method of obtaining photographiccontrasts by means of diazonium compounds described in the co-pendingapplication Ser. No. 612,364 filed May 19, 1932 of de Boer, Dlppel andAlink.

In the above referred to application there is described a novel methodof obtaining photographic contrasts by means of diazonium compoundswhich instead of being based on the production of azo dyes by couplingof a diazonium compound with an azo component-utilized in previouslyknown methods of obtaining diazotypes-utilizes the oxidizing propertiesof cer. tain diazonium compounds. Thereby colored oxidation products areformed from the light-decomposed products of the diazonium compounds.

According to the process of the above referred to application, a carrieris provided with a light sensitive substance which consists of one ormore diazonium compounds of which compounds at least one, upon exposureto actinic light in the presence of water, forms a phenol so substitutedin .the benzene nucleus, that the phenol can be oxidized either by thenon-decomposed portion of that particular diazonium compound or by someother diazonium compound provided on the carrier. A colored compound isthus formed without the addition of an azo component, whereby thediazonium compound oxidizes the phenol produced during the exposure muchmore rapidly than it would couple therewith to form an azo dye.

In this process, as stated in the above application, such diazoniumcompounds have been found especially suitable, which yield after theirexposure polyphenols which are in no way capable of coupling withdiazonium compounds. For example, a suitable compound for printing paperis parahydroxy benzene diazoniumchloride, upon exposure of whichhydroquinone, nitrogen and hydrochloric acid are formed.

7 Another suitable diazonium compound is, for

instance,- '1-hydroxy-2-diazo-4-benzenesulphonic acid;

The process of making heliographic prints by means of a carrier providedwith a light sensitive diazonium compound described in the aboveapplication consists in locally exposing such car- 'rier to a lighthaving a strongly actinic efiect on the light sensitive substance, afterwhich the whole carrier is subjected to a second exposure, this time toa light which is only slightly actinic with regard to the lightsensitive substance of the "carrier, so that part of the diazoniumcompound is converted into a phenol and this phenol is caused to beoxidized by the non-converted portions of the diazonium compound to forma colored oxidation product. The oxidization may be accelerated bymoderate heating to about 80 C. and the formation of contrasts can begreatly promoted by the addition of copper salts, such as coppernitrate. Excellent contrasts are obtained on a positive print made froma positive, for instance from a drawing, if the paper serving as carrieris soaked in a 0.25% alcoholic solution of-1-hydroxy-2-diazo-4-benzene-sulphonic acid, to which 0.55% of coppernitrate is added. After the paper is dried, the print is made byexposing the so treated carrier under the drawing to the light of asuitable highly actinic light source, for

instance a carbon arc lamp, for about 20 seconds, and after suchexposure the paper is exposed to regular light and preferably heated fora certainperiod at about 80 C. Thereby a positive print having a darksteel gray tone is obtained from the drawing.

Thus, as more fully described in the above application, in this methodwhich is. based on the oxidation of the product produced by exposurefrom the diazonium compound by a still unconverted diazonium compound,no substance needs to be added after the exposure, nor needs the printto be subjected to further treatments. The advantages'of this novelmethod are simplicity, low cost and at the same time excellent printsare obtained.

The present invention relates to an improvement in the method ofthe'above application.

As light sensitive carriers, for instance, printing paper, are generallystored for a considerable time prior to their use they are generallykept in closed containers to prevent access of light. It has been foundhowever that a light sensitive carrier, for instance, printing papermade according to the prior invention, when subjected to prolongedstorage in such containers decreased in light-sensitiveness and afterseveral months the paper'loses practically all of itslight-sensitiveness.

Experiments have shown that this loss in lightsensitiveness is not dueto the access of light or oxygen but to moisture either present in thepaper or gradually absorbed from the air even when the container waskept closed or when it was opened (without access of light) for shortperiods to remove some of the paper. Even a small amount of moisture hada considerable deteriorating eflect, which is due to some chemicalreaction probably in the form of the diazonium group being replaced by ahydroxyl group. It was found that when such paper was exposed to avery;damp medium, the annihilation of the diazonium group took placeso-rapidly that the diazonium compound which has been converted by watercould no more be oxidized by the unconverted diazonium compound. Paperwhich had lost all its light-sensitiveness in this way showed apractically white color over its entire surface.

Further experiments showed that if only a small amount of water vapor orwater was allowed to act on such light sensitive paper, its

light sensitiveness could be longer maintained. However, even in thiscase the light-sensitiveness is eventually entirely lost, but in thiscase the paper, after losing its light sensitiveness, showed a darkcolor. This may be due to the oxidation of the gradually producedoxidizable phenol by diazonium compound not yet decomposed by the waterand of which a plentiful supply is still present as the reaction takesplace gradually.

It was found, furthermore, that such sensitized paper will maintain itslight sensitiveness almost indefinitely if it is highly dried and storedin a highly dry atmosphere, this being even the case when oxygen ispresent. On the other hand, an exhausted and air-tightly sealedcontainer would not protect the light sensitiveness of the paper ifwater vapour is present in the container.

The present invention, therefore, relates to a method of drying alight-sensitive material, for instance, heliographic printing paper,made accordingto the invention of the prior application, to remove fromit the moisture to such extent that chemical reactions inducive to thedeterioration of the light sensitive properties of the material beprevented and to maintain said material in such a dry state during itsstorage.

While it is known practice to dry certain types of papers, for instance,light sensitive papers used for printing, and keep them, reasonably dryin storage or dry them before use, a small amount of moisture present insuch papers does not deleteriously influence their properties.

However, in the present instance, the light sensitive material, madeaccording to the invention of the prior applicatiompermanentlydeteriorates in the presence of even a small amount of mo1sture and tomaintain its initial and maximum .light sensitivity it has to be driedand kept dry tained during its storage in such dry condition whereby thedecomposition of the diazonium compound is altogether prevented and thelight sensitiveness of the material made according to the invention ofthe prior application can be maintained to its full extent.

The above definition of the moisture content will be fully understoodfrom the following:

If a so-called air-dried paper is subjected to the well-known dryingprocess of heating it at a temperature between 105 to 110 C. for 24hours, it shows a decrease of between 5 to 6% in weight, such decreasenot exceeding 6.5%.

On the other hand, if such air-dried paper is placed in a containercomprising fresh phosphorus-pentoxide and is maintained in the containerfor 24 hours at a temperature of about 25 0., it shows a decrease inweight of about 8%.

garded as bone dry, and the sensitizedpaper tofulfill the above statedcondition should be deprived from moisture to such extent as to loseabout 7% of its weight compared to its air-dry condition.

According to one method of our invention a suitable paper, after beingsensitized by means of an alcoholic solution of a diazonium compound ofthe nature above described, is dried under vacuum until its moisturecontent has been reduced to the above extent.

Another method provides for the drying of such a sensitized paper in anenclosure which has an atmosphere maintained perfectly dry by a powerfuldrying agent, for instance, by phosphorus-pentoxide.

In a still further method of drying, the sensi-,

tized paper is placed in a container and flushed with a gas, forinstance, nitrogen or air, from which all moisture has been extractedeither by means of a powerful drying medium, for instance,phosphorus-pentoxide, or by freezing the moisture out at a very lowtemperature. For instance, from air moisture can be completely frozenout at about 180 C.

Of if desired, combinations of the above drying processes may be used.

To maintain the paper so dried during its storage in its highly drycondition, weprovide for it containers, for instance glass receptacleswhich are sealed by a moisture-proof compound, for instance, a suitablesealing wax, and which container does not comprise moisture at all orthe moisture content of which is so low that the paper can absorb nosuch quantities of moisture which would increase its moisture contentabove 1%.

Again, the dried light sensitive material may be stored inhermetically-sealed metal boxes or containers consisting of thin metalplates, the edges of which are welded or soldered together, and whichhave been freed from moisture.

It should be pointed out that the generally used wrapping means, forinstance, cardboard containers or paraflin impregnated paper wrappers,which are entirelysuitable containers for other light sensitivematerials, are deficient as containers or wrappers for light sensitivematerial according to the prior application, and even if such lightsensitivematerial has been sharply dried by one of the previouslydescribed methods, sufiicient moisture will gain access to it andgradually destroy its light sensitive properties.

It should be also understood that if the light sensitive material whenplaced in the container is provided with a protective wrapping ofordinary paper or similar material, such wrapping paper has also to bedried to a similar extent as the light sensitive material.

. While prolonged drying under a high temperature might expel sufllcientmoisture from the light sensitive material to reduce its moisturecontent within the above stated limit, drying by heat is as a ruleobjectionable as at elevated temperatures a partial decomposition andoxidization of the diazonium compound takes place.

By the high degree drying and keeping the material insuchhighlydriedcondition, deterioration of the light sensitive material iswholly-prevented, and the contrasts obtained in printing are very sharpwhereby the copied out portions of the print are and remain white. 1 Atthe same time the light sensitiveness of the paper is much greater whenin such highly dry state than in the case when it has a moisture contentexceeding 1% and thus a much shorter exposure can beusedwithhighlydriedpaperthanwith apaper having such higher moisture content, and thisholds irrespective of the time of storage of such D 1 While we havedescribed our invention with reference to. certain examples, it shouldbe well understood that we do not wish to be limited to such, but desirethe appended claims to be con- -strued as broadly as permissible in view01' the prior art.

What we claim is:

1. The method of producing a light-sensitive material comprising adiazonium compound which upon exposure to actinic light in the presenceof water forms a phenol which is oxidized by the unconverted portions ofa diazonium compound and forms a colored compound without the additionof an azo-component, comprising the steps 01' providing a carrier withsaid diazonium compound and removing from said material the moisture sothat it forms less than 1% of the weight of the material.

2. The method of producing a light-sensitive material comprising adiazonium compound which upon exposure to actinic light in the presenceoi water forms a phenol which is oxidized by the unconverted portions ofa diazonium compound and forms a colored compound without the additionor an azo-component, comprising the steps of providing a carrier with-said diazonium compound andremoving from said material the moisture sothat it forms less than 1% of the weight the material and enclosing saidmaterial in an air tightly sealed container having a substantiallymoisture-tree atmosphere.

3.- The method 01 producing a light-sensitive material comprising adiazonium compound which upon exposure to actinic light in the presenceof water forms a phenol which is oxidized by the unconverted portions ofa diazonium compound and forms a colored compound without the additionof an azo-component; comprising the steps of providing a carrier withsaid diazonium compound and placing said material in a closed container,evac said container to remove from said material e moisture so that it;forms less than 1% o! the weight of the marial.

4. The method of producing a light-sensitive material comprising adiazonium compound which upon exposureto actinic light in thepresmaterial comprising a diazonium compound which umn exposure toactinic light in the presence 01 water forms a-phenol which is oxidizedby the unconverted portions of a diazonium compound and forms a coloredcompound without a the addition 01' an aha-component, com

the steps of providing a carrier with said diazonium compound and to adrying operation by flushing it with a gas from which the moisture hasbeen removed by freezing it out at low temperature to remove irom'saidmaterial the moisture so that it iorms less than 1% of the weight of thematerial.

6; The method of producing a light-sensitive material comprising adiazonium compound which upon exposure to actinic light in the presenceof water iorms a phenol which is oxidized by the unconverted portions ofa diazonium compound and forms a colored compound without the additionof an azo-component, the steps of providing a carrier with saiddiazonium compound and subjecting said material to a drying operation byflushing it with a gas from which the-moisture has been removed byfreezing it out at about 180 C. to remove from said material; themoisture so that it forms less than 1% of the weight of the material '1.A light-sensitive material comprising a carrier such as paper providedwith a light-sensitive layer, in which the light sensitive substancecomprises a diazonium compound which upon exposure to actinic light inthe presence oi water forms primarily a phenol so substituted in thebenzene subjecting said material.

comprising nucleus that this phenol can be oxidized byan 13 unconverteddiazonium compound to form a colored compound without the addition oi anazo component, said material'having a moisturecontent less than 1%..

ROELOF JAN HENDRIX ALINK. JAN HENDRIX pl BOER.

